[GRASSLIST:5104] Re: adding stream axis to dem

[Maciek Sieczka]

> I´m trying to improve the quality of a dem and I think that adding the 
> axis of the rivers will be fine in order to do it... but I don´t know how 
> to do it.

If I understand your problem the following paper should give you a hint:

Cebecauer, Hofierka, Súri, 2002, Processing digital terrain models by
regularized spline with tension: tuning interpolation parameters for
different input datasets. Proceedings of the Open source GIS - GRASS users
conference 2002 - Trento, Italy, 11-13 September 2002

However doing this in *.surf.rst requires having an accurate elevation data 
along the stream distributed evenly and dense. As this requirement is hard 
to fullfill, and often simply cannot be, you may try to use the 
CatchmentSIMGIS (freeware, Windows only) to help you to determine the 
elevation along the streams. The DEM it produces looks awfull when compared 
to a well-done *.surf.rst output, although it's "hydrologicaly correct" and 
rather reliable for the valley bottoms and ridges elevations, if you include 
their shapes in the interpolation. So you can sample such a DEM along the 
valleys and rigdes shapes to enhance your elevation data for the *.surf.rst 
input. I guess you could also utilize the Topogrid/Anudem in the same way 
but it COSTS.

What do you Guys think of it?

Maciek